This invention relates to an electrophotographic plate excellent in electrophotographic properties and durability.
Heretofore, inorganic photoconductive substances such as selenium, zinc oxide, titanium oxide, cadmium sulfide, etc. have mainly been used as photosensitive materials in electrophotographic materials applying photoconductive substances as photosensitive materials. But these materials are generally strongly poisonous and cause a problem in their disposal.
On the other hand, photosensitive materials using organic photoconductive compounds are generally weak in toxicity compared with the inorganic photoconductive substances and advantageous in transparency, flexibility, light weight, surface smoothness, price, etc. Thus, the use of organic photoconductive compounds has widely been studied. Above all, photosensitive materials consisting of multi-layer having separated charge generating function and charge transport function have been developed rapidly, since they can remarkably increase sensitivity which was a great defect of prior art photosensitive materials using organic photoconductive compounds.
When these photosensitive materials using organic photoconductive compounds are applied to electrophotographic equipments, for example, employing the Carlson process and subjected to repeated charging, exposing and developing (or "charge, exposure and development"), it is necessary to clean (remove) toners slightly adhered to and remaining on the surface of photosensitive material with a blade or brush. By repeating this cleaning step, the surface of photosensitive material is worn and damaged, which results in making transferred images unclear and sometimes bringing about peeling of a charge transport layer and a charge generating layer so as to shorten the life of photosensitive material remarkably.
In order to improve the durability, the formation of a protective layer consisting essentially of a polymer such as nitrocellulose, acetylnitrocellulose, polyvinylbutyral, polycarbonate, polystyrene, polyeter, polyurethane, polyamide, poly-n-tutyl methacrylate, etc., on the surface is proposed, for example in U.S. Pat. No. 4,469,771 and German Laid-Open (DE-OS) No. 2,452,622. But the prior art protective films are not sufficient in wear resistance and have a defect in that an increase in residual potential in electrophotographic properties and lowering in the sensitivity easily take place. Therefore, the development of a protective layer having high wear resistance without lowering electrophotographic properties has been desired.